1. Field of the Invention
The present invention relates generally to a process for forming intermediate grade manganese concentrate from low grade manganiferous ore and, more particularly, to such a process which chemically transforms low grade manganiferous ore to a moderately magnetic manganese-iron spinel which is amenable to concentration by low (standard) intensity magnetic separation.
2. Description of the Prior Art
In most recent history, the quest for discovery has been guided more out of a need than out of adventure. For example, man has discovered that many of the earth's critical minerals are in finite supply. For the United States, these minerals include chromium, platinum and manganese. As is apparent, these minerals are critical to our nation's economic stability and national security. On Jan. 7, 1987, manganese was certified by the U.S. Department of State as a strategic mineral essential for the economy and defense of the United States that is unavailable in adequate quantities from reliable and secure domestic suppliers. The problem created by this unavailability is aggravated since there is currently no satisfactory substitute for manganese in its major applications.
At present, the United States depends totally on imports for its manganese requirements. The main sources of manganese imports are the Republic of South Africa, France, Gabon and Brazil. Manganese ore containing between 35 and 54 per cent manganese and ferromanganese containing between 74 and 95 per cent manganese are imported for domestic consumption. The principal use of manganese is for the production of iron and steel, and its demand for this purpose far exceeds all other demands. Manganese is used by the steel industry chiefly in the form of ferromanganese or silicomanganese. Also, some producers of pig iron add manganese ore or manganiferous ore to their furnace burden.
Domestically, one of the largest deposits of manganese ore may be found in the Cuyana Range located in central Minnesota. These manganese ore deposits occur predominantly as carbonate and oxide minerals, and represent the most promising domestic land resource. These ores consist of impure oxides, principally pyrolusite, a lesser amount of rhodochorosite, goethite, hematite, magnetite and siliceous materials including quartz. Resource estimates from the 1981 Minnesota geological survey indicate that the Cuyana Range contains a minimum of 176 million long ton of marginally economic manganiferous rock with an average grade of 10.5 weight per cent manganese. It is estimated that the calculated 18.5 million long ton of manganese contained in the manganiferous rock could supply this country's needs for this important and strategic ore for approximately 30 years. Also, an additional resource of 6.9 million long ton of manganese is available in lower grade deposits.
Although the manganiferous rock present in the Cuyana Range is itself presently extractable by current surface mining techniques, the manganese in the manganiferous rock is not economically recoverable utilizing presently known separation processes. In addition, it is apparent that even if the manganese was recoverable from the manganiferous rock, the concentration of manganese itself is only marginally satisfactory for use in domestic iron and steel applications. As a result, the need to import manganese ore for domestic consumption continues.
Consequently, there is a need for a process for economically recovering manganese ore from manganiferous rock which also converts the low grade ore recovered to an intermediate grade manganese concentrate for subsequent use in iron and steel applications.